Gas turbine combustors work under extreme conditions, and as such have increasingly complex cooling systems, designed to maximise cooling and minimise cooling air use. In general, air management is an important consideration in combustor design, since air is used both as an oxidiser in the combustion process and to provide cooling to hot gas path components of the combustor. In order to ensure maximum efficiency of the gas turbine engine, leakages and pressure drops in air distribution should be minimised. In addition, it is important to minimise the complexity of the system for maintenance, thermal expansion and accessibility of hot gas path components. Increasing requirements in gas turbine efficiency demand continuing improvement of components to maximise performance. In light of these various requirements, it has been appreciated that changes could be made to improve combustor performance.